Aluminium Wool (magnesium alloy)

This squeaky, crunchy tangle of pale silver-blue filaments is aluminium wool; used for everything from polishing aerospace components, creating soft shading in Renaissance-style metalpoint drawings, and stopping mice from squeezing through tiny gaps in our skirting boards. 

This metallic swarf is fragile, flexible and yet surprisingly razor-edged, motivating its manufacturers to warn us to ‘always cut’ and ‘do NOT tear’ their material. It is made by pulling strong aluminium wires through a series of smaller and smaller shaving dies, a type of circular cutting tool that peels uniform and very thin strands of metal off their surface. These shavings coil together into a loose, airy bundle that is lightweight and soft to the touch, but abrasive and relatively strong when rubbed against a surface. The sharp edges of each tiny filament scrape away at grime, varnish and other surface finishes, and the airy gaps between them trap abraded material inside the wool to stop it clogging up the surfaces. 

Aluminium wool is used instead of other metal wools (like our stainless steel wool) when the surface that needs abrading is also a non-ferrous metal, or if it is a relatively soft and easily scratchable. This is because stainless steel wool is generally tougher and more abrasive than the same grade of aluminium wool, but also because metal wools can leave behind microscopic particles of themselves that cause galvanic corrosion in metals that have a different ‘electrochemical potential’ to them. 

A metal’s electrochemical potential is a measure of how likely it is to lose or gain electrons when it comes into electrical contact with a dissimilar material. Aluminium is a highly electrochemically reactive metal, with a tendency to give up its electrons willy nilly to other materials when prompted. This sometimes works in aluminium’s favour: it reacts readily with oxygen in the air to quickly develop a transparent, protective and self-healing layer of aluminium oxide that gives it a good level of corrosion-resistance to a broad range of chemicals (with the exception of strong acids and alkalis). However, this same property makes galvanic corrosion one of aluminium’s particular Achilles heels’. 

Galvanic corrosion occurs when two dissimilar metals are connected by a conductive medium, like salty water, that brings them into electrical contact with each other. If one metal is more reactive than the other, electric charges flow through the water from one metal to the other, with the two metals effectively acting like the anode and cathode in a battery cell. When aluminium and stainless steel are submerged together in water, aluminium tends to lose its electrons to stainless steel and corrodes, losing its structural strength. This has the potential to create huge problems for aluminium used in aircraft fuselage, wings and engine components that are often subjected to damp and corrosive atmospheres. Aerospace engineers have to take particular care to ensure that dissimilar metals are not used next to each other in aircraft, or are separated by washers, paints and other insulating barrier layers. 

This metallic candyfloss isn’t only useful for cleaning and polishing: aluminium’s malleability has made it a recent addition to the metalpoint artist’s toolkit. Metalpoint is a line drawing technique that was popularised in the 15th century and has seen various revivals from the 19th to the 21st centuries. Before graphite pencils were invented, 15th century artists like Albrecht Dürer and Leonardo da Vinci used sticks of soft and malleable metals like silver and lead to create fine sketches. As these metal sticks were dragged over a ‘toothy’ surface (one prepared with an abrasive and porous coating), microscopic particles sheared off and were deposited on the paper. The fine and luminous traces of metal left behind could not be erased, and often oxidised and changed colour over time. As it wasn’t invented until the 19th century, aluminium wasn’t originally used for metalpoint, but contemporary artists like Susan Schwalb and Jasper Johns who revived the technique use wool like this for soft shading, alongside silver spoons, nails and a variety of other metal drawing tools.